Protocol stack
Encyclopedia
The protocol stack is an implementation of a computer network
ing protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them.
Individual protocols within a suite are often designed with a single purpose in mind. This modularization
makes design and evaluation easier. Because each protocol module usually communicates with two others, they are commonly imagined as layers in a stack of protocols. The lowest protocol always deals with "low-level", physical interaction of the hardware. Every higher layer adds more features. User applications usually deal only with the topmost layers (see also OSI model
).
In practical implementation, protocol stacks are often divided into three major sections: media, transport, and applications. A particular operating system
or platform will often have two well-defined software interfaces: one between the media and transport layers, and one between the transport layers and applications.
The media-to-transport interface defines how transport protocol software makes use of particular media and hardware types ("card drivers"). For example, this interface level would define how TCP/IP
transport software would talk to Ethernet
hardware. Examples of these interfaces include ODI
and NDIS
in the Microsoft Windows
and DOS
environment.
The application-to-transport interface defines how application programs make use of the transport layers. For example, this interface level would define how a web browser
program would talk to TCP/IP transport software. Examples of these interfaces include Berkeley sockets
and System V STREAMS
in the Unix
world, and Winsock
in the Microsoft world.
[A] [B]_____[C]
Imagine three computers: A, B, and C. A and B both have radio equipment, and can communicate via the airwaves using a suitable network protocol (such as IEEE 802.11
.) B and C are connected via a cable, using it to exchange data (again, with the help of a protocol, for example Ethernet). However, neither of these two protocols will be able to transport information from A to C, because these computers are conceptually on different networks. One, therefore, needs an inter-network protocol to "connect" them.
One could combine the two protocols to form a powerful third, mastering both cable and wireless transmission, but a different super-protocol would be needed for each possible combination of protocols. It is easier to leave the base protocols alone, and design a protocol that can work on top of any of them (the Internet Protocol
is an example.) This will make two stacks of two protocols each. The inter-network protocol will communicate with each of the base protocol in their simpler language; the base protocols will not talk directly to each other.
A request on computer A to send a chunk of data to C is taken by the upper protocol, which (through whatever means) knows that C is reachable through B. It, therefore, instructs the wireless protocol to transmit the data packet to B. On this computer, the lower layer handlers will pass the packet up to the inter-network protocol, which, on recognizing that B is not the final destination, will again invoke lower-level functions. This time, the cable protocol is used to send the data to C. There, the received packet is again passed to the upper protocol, which (with C being the destination) will pass it on to a higher protocol or application on C. Often an even higher-level protocol will sit on top, and incur further processing.
An example protocol stack and the corresponding layers:
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
ing protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them.
Individual protocols within a suite are often designed with a single purpose in mind. This modularization
Modularity (programming)
Modular programming is a software design technique that increases the extent to which software is composed of separate, interchangeable components called modules by breaking down program functions into modules, each of which accomplishes one function and contains everything necessary to accomplish...
makes design and evaluation easier. Because each protocol module usually communicates with two others, they are commonly imagined as layers in a stack of protocols. The lowest protocol always deals with "low-level", physical interaction of the hardware. Every higher layer adds more features. User applications usually deal only with the topmost layers (see also OSI model
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
).
In practical implementation, protocol stacks are often divided into three major sections: media, transport, and applications. A particular operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
or platform will often have two well-defined software interfaces: one between the media and transport layers, and one between the transport layers and applications.
The media-to-transport interface defines how transport protocol software makes use of particular media and hardware types ("card drivers"). For example, this interface level would define how TCP/IP
Internet protocol suite
The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...
transport software would talk to Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
hardware. Examples of these interfaces include ODI
Open Data-Link Interface
The Open Data-Link Interface , developed by Apple and Novell, serves the same function as Microsoft and 3COM's Network Driver Interface Specification . Originally, ODI was written for NetWare and Macintosh environments. Like NDIS, ODI provides rules that establish a vendor-neutral interface between...
and NDIS
Network Driver Interface Specification
The Network Driver Interface Specification is an application programming interface for network interface cards . It was jointly developed by Microsoft and 3Com Corporation, and is mostly used in Microsoft Windows, but the open-source NDISwrapper and Project Evil driver wrapper projects allow...
in the Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
and DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
environment.
The application-to-transport interface defines how application programs make use of the transport layers. For example, this interface level would define how a web browser
Web browser
A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content...
program would talk to TCP/IP transport software. Examples of these interfaces include Berkeley sockets
Berkeley sockets
The Berkeley sockets application programming interface comprises a library for developing applications in the C programming language that perform inter-process communication, most commonly for communications across a computer network....
and System V STREAMS
STREAMS
In computer networking, STREAMS is the native framework in Unix System V for implementing character devices.STREAMS was designed as a modular architecture for implementing full-duplex I/O between kernel or user space processes and device drivers. Its most frequent uses have been in developing...
in the Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
world, and Winsock
Winsock
In computing, the Windows Sockets API , which was later shortened to Winsock, is a technical specification that defines how Windows network software should access network services, especially TCP/IP. It defines a standard interface between a Windows TCP/IP client application and the underlying...
in the Microsoft world.
General protocol suite description
T ~ ~ ~ T[A] [B]_____[C]
Imagine three computers: A, B, and C. A and B both have radio equipment, and can communicate via the airwaves using a suitable network protocol (such as IEEE 802.11
IEEE 802.11
IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent...
.) B and C are connected via a cable, using it to exchange data (again, with the help of a protocol, for example Ethernet). However, neither of these two protocols will be able to transport information from A to C, because these computers are conceptually on different networks. One, therefore, needs an inter-network protocol to "connect" them.
One could combine the two protocols to form a powerful third, mastering both cable and wireless transmission, but a different super-protocol would be needed for each possible combination of protocols. It is easier to leave the base protocols alone, and design a protocol that can work on top of any of them (the Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
is an example.) This will make two stacks of two protocols each. The inter-network protocol will communicate with each of the base protocol in their simpler language; the base protocols will not talk directly to each other.
A request on computer A to send a chunk of data to C is taken by the upper protocol, which (through whatever means) knows that C is reachable through B. It, therefore, instructs the wireless protocol to transmit the data packet to B. On this computer, the lower layer handlers will pass the packet up to the inter-network protocol, which, on recognizing that B is not the final destination, will again invoke lower-level functions. This time, the cable protocol is used to send the data to C. There, the received packet is again passed to the upper protocol, which (with C being the destination) will pass it on to a higher protocol or application on C. Often an even higher-level protocol will sit on top, and incur further processing.
An example protocol stack and the corresponding layers:
| Protocol | Layer |
|---|---|
| HTTP | Application Application layer The Internet protocol suite and the Open Systems Interconnection model of computer networking each specify a group of protocols and methods identified by the name application layer.... |
| TCP Transmission Control Protocol The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP... |
Transport Transport layer In computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols... |
| IP Internet Protocol The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite... |
Internet Internet layer The internet layer or IP layer is a group of internetworking methods in the Internet protocol suite, commonly also called TCP/IP, which is the foundation of the Internet... |
| Ethernet Ethernet Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies.... |
Link Link Layer In computer networking, the link layer is the lowest layer in the Internet Protocol Suite , the networking architecture of the Internet . It is the group of methods or protocols that only operate on a host's link... |
| IEEE 802.3u | Physical Physical layer The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY.... |
See also
- Cross-layer optimizationCross-layer optimizationCross-layer optimization is an escape from the pure waterfall-like concept of the OSI communications model with virtually strict boundaries between layers. The cross layer approach transports feedback dynamically via the layer boundaries to enable the compensation for e.g...
- G.hnG.hnG.hn is the common name for a home network technology family of standards developed under the International Telecommunication Union's Standardization arm and promoted by the HomeGrid Forum...
- Hierarchical internetworking modelHierarchical internetworking modelThe Hierarchical internetworking model, or three-layer model, is a network design model first proposed by Cisco. Thethree-layer model divides enterprise networks into three layers: core, distribution, and access layer. Each layer provides different...
- Internet protocol suiteInternet protocol suiteThe Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...
- Network protocol design principles
- OSI protocol suite
- Service layerService layerIn intelligent networks and cellular networks, service layer is a conceptual layer within a network service provider architecture. It aims at providing middleware that serves third-party value-added services and applications at a higher application layer...
- Solution stackSolution stackIn computing, a solution stack is a set of software subsystems or components needed to deliver a fully functional solution, e.g. a product or service....
- TCP/IP model
- WAP protocol suite
- X.25 protocol suite